Heavy rains replenish groundwater supplies in Africa

13 November 2012

Intensive rainfall in East Africa can result in widespread flooding but may have a silver lining in the form of replenishing vital groundwater supplies.

New research by Dr Richard Taylor (UCL Geography) and colleagues from Sussex University, the Tanzanian government and British Geological Survey in semi-arid Tanzania has found that very heavy rainfall that accompanies the El Niño phenomenon is vital for recharging underground aquifers in the region.

In central Tanzania, there is near total dependence upon groundwater resources for public water supplies. The team’s findings, published in the latest edition of Nature Climate Change, show that groundwater resources are replenished, on average, just twice each decade. Although pumping of groundwater from wells depletes the aquifer outside of these events, replenishment from periods of extreme rainfall is so far sufficient to sustain intensive groundwater use.

This research, supported by the Department for International Development (DFID), builds on work by members of this team published earlier this year that revealed that freshwater stored in subsurface aquifers greatly exceeds that which is found at the surface in lakes and rivers. However, a key uncertainty was replenishment rates. These new findings have begun to provide an answer.

“East and southern Africa experiences the most variable rainfall and river flow on the planet. Reliable, safe sources of freshwater found underground are consequently of critical importance,” said Dr Taylor. “Variability in rainfall is projected to increase in the future – threatening food production and increasing the risk of flooding yet the long-term historical record from Tanzania that we’ve compiled indicates that this more variable rainfall favours replenishment of groundwater resources.”

He added that more work is required to define how and where heavier rains replenish groundwater but said that communities and their farmers may be able to adapt to climate variability and change by exploiting these reservoirs and promoting rainwater harvesting schemes that enhance the capture and storage of heavy rainfalls.